I particurly liked merlyn's solution:

@copy = @$r;
while (my @pair = splice @copy, 0, 2) {
  push @$r2, [@pair];
}
[download]

However, I'll modify it slightly to show everyone what I came up with. (Maybe it's just me, but bit-wise operators always seem to pop-up in my code ... probably where they shouldn't :)

@copy = @$r;
# I guess you know that your array will work for this, but
# it may be desirable to check (especially for n-'tuples')
# that the array is divisible by 2 (or n).  I guess that
# depending on what you're expecting this can be done on a
# all or nothing basis, or inside the loop

while (0..$#copy) {
  next if $_&1; # this skips all odds (you used a mod in
                # your original I think).  To expand to more
                # 'tuples', you'd have to change this to
                # next if $_%n
  push @$r2, [$copy[$_],$copy[$_+1]];
}
[download]